Multi-phase induction heating device

ABSTRACT

An induction heating device comprising a frame generally defining a loading receiving chamber and at least three overlapping, electrically insulated, induction heating coils adapted to be magnetically coupled with a load within the chamber. Each of the induction heating coils has a series of repeating loops comprising two spaced, generally parallel legs, with the plane defined by the parallel legs of each loop and between these legs being generally exterior of the chamber.

O United States Patent [151 3,691,339 Cachat [451 Sept. 12, 1972MULTI-PHASE INDUCTION HEATING 2,678,371 5/1954 Andrew ..336/181 X DEVICE2,471,777 5/1949 Reinartz ..336/ 181 X R24,698 9/1959 Logan et al..2l9/l0.79 X

72 I t F. l 1 Cleveland Ohm 2,849,584 8/1958 Tudbury ..219/10.7s AsslgnwPark-Ohio Industries, I Cleve- 3,379,962 4/1968 Kasper ..l3/26 x land,Ohio [22] Filed: May 7, 1971 Primary Examiner-J. V. Truhe AssistantExammer-B. A. Reynolds PP N04 141,676 Attorney--Meyer, Tilberry and Body521 US. Cl. ..219/1o.s7, 219/1035, 219/1019 ABSTRACT [51] Illt. Cl...ll05b 9/02 An induction heating device comprising a frame [.58] newkrch'zlgl 10-57; generally defining a loading receiving chamber and at27; 336/171 181; 310/184 207; least three overlapping, electricallyinsulated, induc- 318/131 tion heating coils adapted to be magneticallycoupled R f ed with a load within the chamber. Each of the induction 1 eheating coils has a series of repeating loops comprising UNITED STATESPATENTS two spaced, generally parallel legs, with the plane defined bythe parallel legs of each loop and between 1,920,325 8/1933 Schmidt..l3/26 these legs being generally exterior f h h 509,705 11/1893Threlfall ..318/131 X 2,005,901 6/1935 Long ..l3/26 X 1 Claim, 4 DrawingFigures l 3 A 2 4 3 A B A B I @(S LWQ/( j C /20 ll'" -2 u- 6 l J 3 Q Blo PATENTEDSEP 12 I972 I I I I f ql I I I I I I I I 1 I I I I I I ll:

I l I l INVENTOR. JOHN F. CACHAT ATTORNEYS BY Mew, 744 8 BodyMULTI-PIIASE INDUCTION HEATING DEVICE This invention relates to the artof induction heating and more particularly toa multi-phase inductionheating device.

The invention is particularly applicable for inductively heating largeloads such as heavy billets or ingots and it will be described withparticular reference thereto; however, it should be appreciated that theinvention has much broader applications and may be used in otherinduction heating installations, especially melting metal and holdingmolten metal.

In rolling mill operations, it is necessary to heat large ingots orbillets to a temperature sufficiently high for subsequent rolling. Avariety of systems have been employed for this heating operation. Forinstance, it is somewhat common to place the ingots within a gasfiredsoaking furnace. After several hours, the ingot is through heatedsufficiently for rolling. This process is relatively slow and results inan excessive amount of scale on the outer surface of the ingot. Suchscale can detrimentally affect the ultimate rolled product. To overcomethese difficulties, it has been suggested to heat inductively the ingotby placing the ingot within a multi-turn induction heating coil. Whenthe coil is energized, the magnetic coupling between. the ingot and thecoil causes current flow within the ingot which creates R heating. Thisinduction heating process results in less scale and decreases theheating time necessary for bringing the ingot up to rolling temperature.However, the induction heating coil includes a plurality of turnssurrounding the workpiece and the reactance within the coil issubstantially high. When a single coil is placed around the ingot, it isconnected onto one phase of an incoming polyphase power source, and thebalance of the polyphase system is detrimentally affected. This problemis substantially increased when the power required is high, such asexperienced in ingot heating. Consequently, there has been considerableeffort devoted to devices for balancing the polyphase or three phasepower source when induction heating is used for raising the temperatureof an ingot. In some cases, dummy loads are employed. In otherinstances, three separate, axially spaced coils are placed around theingot with each coil being in one phase of the polyphase source. Thesearrangements have resulted in a better balance of the three phasesource; however, they do have certain disadvantages. Dummy loads createlosses. The use of three separate axially spaced coils-providesdifferent heating along the length of the billet. Also, if thepermeability along the billet changes, imbalance can be created from onecoil to the other.

All of these disadvantages and others have been overcome by the presentinvention wherein an induction heating installation utilizes three ormore overlapped coils each of which is connected toone phase of apolyphase source and are wound around the load in a configurationgenerally matching the winding of an electric motor stator.

In accordance with the present invention, there is provided an inductionheating device comprising a frame defining a load receiving chamber andat least three overlapping, electrically insulated, induction heatingcoils adapted to be magnetically coupled with a load in the chamber.Each of the induction heating coils has a series of repeating loopscomprising two spaced, generally parallel legs, with the plane definedby the parallel legs of each loop and between these legs being generallywithin the frame and exterior of the chamber. Means are provided forconnecting one phase of a polyphase source to each of these inductionheating coils.

By constructing an induction heating device in accordance with the abovedescription, the several loops of the overlapped coils include parallellegs which are not on opposite sides of the load. The load is within achamber surrounded by the series of loops similar to the loops foundwithin the stator of an electric motor. In this manner, each of thephases is accurately balanced because all corresponding portions of eachcoil within the loop are generally exposed to the same portionof theload being heated. This construction allows a large number of coilswhich will create a relatively small driving force on the load itselfduring the heating operation.

In accordance with another aspect of the invention, successive loops ina given induction heating coil can have opposite hand winding so thatany motive force created by one loop is cancelled by an adjacent loop.When such an induction heating device is employed for melting or holdingmolten metal, the spaced legs of each loop create a substantiallyreduced stirring action even though cycle current is used.

The primary object of the present invention is the provision of aninduction heating device using at least three overlapped coils, whichdevice results in a balanced load for a polyphase source connectedthereto.

Another object of the present invention is the provision of an inductionheating device using at least three overlapped coils, which deviceresults in uniform heating ofa load within the device.

Yet another object of the present invention is the provision of aninduction heating device using at least three overlapped coils, whichdevice reduces stirring action when used for metal melting or holdingmolten metal.

These and other objects and advantages will become apparent from thefollowing description taken together with the accompanying drawings inwhich:

FIG. 1 is a wiring diagram showing the application of the presentinvention;

FIG. 2 is a top cross sectional view showing the preferred embodiment ofthe present invention;

FIG. 3 is a side elevational view taken generally along line 3-3 of FIG.2; and,

FIG. 4 is a schematically represented layout of the coils used in thepreferred embodiment of the present invention.

Referring now to the drawings wherein the showings are for the purposeof illustrating, schematically, the preferred embodiment of the presentinvention and not for the purpose of limiting same, FIG. 1 illustrates athree phase power supply having input leads L L and L and Y-connectedcoils l0, 12, 14 defining phases A, B, and C, respectively. Inaccordance with the present invention, the coils 10, I2, 14 are all usedto heat inductively a workpiece B in the form of a slab or ingot. Thisworkpiece, or load, could also be metal for melting or molten metal tobe held in the molten state.

In accordance with the present invention, the induction heating coils10, 12, and 14 have a particular configuration which is illustrated inFIGS. 2-4. A frame 20 formed from a high permeability material includesa plurality of elongated slots 22 defined between elongated ribs 24.These ribs have outer pole surfaces 26 facing an inner workpiecereceiving chamber 30 into which the workpiece or load B is placed.Within the slots there are provided a plurality of parallel conductors AB C A B C etc. These parallel legs are formed by winding an inductionheating conductor in a pattern which creates a series of repeating loopseach of which has two of the parallel spaced legs. FIG.'4 illustrates apreferred type of winding pattern wherein the coil is shown in solidline, the coil 12 is shown in dashed line, and the coil 14 is shown indotted line. It is noted that the individual coils, as shown in H6. 4,include alternate left and right hand loops as they extend around theworkpiece receiving chamber 30. This par ticular type of alternate handwinding configuration is useful to reduce the magnetomotive forceerierted on the load during heating. One loop tends to drive the load inone direction and an adjacent loop cancels that tendency. However, itiswithin the contemplation of the present invention to wind the coils l0,l2, and 14 around the frame in the same hand, since the magnetomotiveforce exerted on the load will generally be somewhat low and can becounteracted by the weight of the load.

By constructing the coils 10, 12 and 14 in accordance with the presentinvention, the coils do not contain loops which circle the workpiece asis standard practice in the induction heating art. Since correspondinglegs, i.e. A 13,, C etc., of the three coils 10, 12, and 14 are adjacenteach other, the corresponding legs are subjected to substantially thesame impedance during the heating operation. This provides an efficientmanner for balancing the load in all three phases of the system, asshown in FIG. 1. By using a plurality of legs in this manner, there is areduction in the stirring action caused during melting of molten metalbecause adjacent flux fields are out of phase. There is no accumulationof flux field phases which can impart a large stirring action upon themolten metal when low frequency is used.

In accordance with the invention, sufficient number of loops are formedin the coils l0, l2, and 14 to provide at least about 24 pole surfacesbetween adjacent loops. This number of pole faces creates a uniformheating of the workpiece. The coils are formed from hollow conductors toallow passage of coolant therethrough.

Having thus defined my invention, I claim:

1. An induction heating device comprising a frame defining a loadreceiving chamber; three overlapping, electrically insulated, inductionheating coils adapted to be magnetically coupled witha load in saidchamber, each of said induction heating coils having a series ofrepeating loops comprising two spaced, generally parallel legs with theplane defined by said parallel legs of each loop and between said legsbeing generally within said frame and exterior of said chamber; meansfor connecting one phase of a three phase source to each of saidinduction heating coils; and, said series of loops of each of said-coilsincluding a plurality of alternate right hand arid le ft h and wo undloops.

1. An induction heating device comprising a frame defining a loadreceiving chamber; three overlapping, electrically insulated, inductionheating coils adapted to be magnetically coupled with a load in saidchamber, each of said induction heating coils having a series ofrepeating loops comprising two spaced, generally parallel legs with theplane defined by said parallel legs of each loop and between said legsbeing generally within said frame and exterior of said chamber; meansfor connecting one phase of a three phase source to each of saidinduction heating coils; and, said series of loops of each of said coilsincluding a plurality of alternate right hand and left hand wound loops.